driver model: constify attribute groups

Let attribute group vectors be declared "const".  We'd
like to let most attribute metadata live in read-only
sections... this is a start.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/mtd/mtdcore.c

@@ -217,7 +217,7 @@ struct attribute_group mtd_group = {
 	.attrs		= mtd_attrs,
 };
 
-struct attribute_group *mtd_groups[] = {
+const struct attribute_group *mtd_groups[] = {
 	&mtd_group,
 	NULL,
 };